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Research Papers: Numerical Methods

A Proposal for a Simplified Assessment Procedure to API-579 Standard

[+] Author and Article Information
Youssef A. F. Hafiz

Department of Mechanical Engineering,
School of Sciences and Engineering,
The American University in Cairo,
P.O. Box 74, New Cairo,
Cairo 11835, Egypt
e-mail: ysfouad@aucegypt.edu

Maher Y. A. Younan

Professor of Mechanics and Design
Associate Dean for Undergraduate Studies,
School of Sciences and Engineering,
The American University in Cairo,
P.O.Box 74, New Cairo,
Cairo 11835, Egypt
e-mail: myounan@aucegypt.edu

Hany F. Abdalla

Assistant Professor of Mechanical Design
and Solid Mechanics
Department of Mechanical Engineering,
British University in Egypt,
Cairo 11837, Egypt
e-mail: hany_f@aucegypt.edu; hany.fayek@bue.eg.edu

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 15, 2014; final manuscript received August 18, 2014; published online March 25, 2015. Assoc. Editor: Reza Adibi-Asl.

J. Pressure Vessel Technol 137(3), 031007 (Jun 01, 2015) (8 pages) Paper No: PVT-14-1067; doi: 10.1115/1.4028425 History: Received April 15, 2014; Revised August 18, 2014; Online March 25, 2015

The objective of this research paper is to propose, to API 579 standard, a simplified assessment procedure for shakedown limit load determination. The proposed assessment procedure applies the Simplified Technique, replacing the existing iterative elastic–plastic API 579 assessment procedures. The technique applies only two analyses (elastic and elastic–plastic) to determine the elastic shakedown limit. The shakedown limit load is determined from the residual stress that is calculated from the scaled elastic stress and subtracted from the elastic–plastic. Finally, to determine the shakedown limit from the residual stress calculated. For the purpose of validating the new assessment procedure to be applied to locally thinned-wall components, the shakedown boundary of a locally thinned-wall pipe-branch connection subjected to a spectrum of steady internal pressures and cyclic bending moments is generated. The results of the proposed assessment procedure are successfully verified against the existing API 579 elastic and elastic–plastic assessment procedures. A parametric study is performed through changing both the depth and location of the local wall thinning within the pipe-branch connection. The results of the parametric study show good agreement in the shakedown limit boundary results with the API 579 elastic–plastic stress analysis procedure.

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References

Figures

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Fig. 1

Locally thinned wall pipe-branch connection geometry and boundary conditions

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Fig. 2

Pipe-branch connection FE model and locations of local wall thinning is shaded in in-plane and out-of-plane cases

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Fig. 3

FE mesh of straight pipe with external local wall thinning (verification study)

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Fig. 4

Comparison of results of area replacement method versus limit analysis method versus developed FE model

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Fig. 5

In-plane shakedown limit boundary when the local wall thinning lies on the run-pipe (dwt/t: local wall thinning depth to total thickness ratio)

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Fig. 6

Out-of-plane shakedown limit boundary when local wall thinning lies on the run-pipe

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Fig. 7

In-plane shakedown moment limit boundary when the local wall thinning lies on the branch

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Fig. 8

Out-of-plane shakedown moment limit boundary when the local wall thinning lies on the branch

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Fig. 9

The effect of the local wall thinning depth on the in-plane and out-of-plane shakedown bending moments, when it lies on the branch

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Fig. 10

The effect of the local wall thinning depth on the shakedown pressure, when it lies on the branch at max tension side of in-plane and out-of-plane situations

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Fig. 11

Equivalent stress versus equivalent plastic strain curve of reversed plasticity behavior

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Fig. 12

von Mises stress versus equivalent plastic strain curve of ratcheting behavior

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